Fishing tool

ABSTRACT

A fishing tool for cable-based retrieval of equipment from a borehole comprises a seat cone, an inner spring that tensions the seat cone, a locking cone that is arranged external to the locking cone and which is tensioned by an outer spring, and at least one latch that is pivotal to a position for gripping the equipment by movement of the seat cone and the locking cone with the aid of the respective springs.

The present invention relates to a fishing tool for cable-based retrieval of equipment from a borehole.

When drilling for oil both onshore and offshore, there is often a need to pull out the drill string, which consists of pipe sections that are screwed together, and the associated bottom drill bit. During pull-out, i.e., the tripping operation, it is most usual that three such connected pipe sections, often referred to as a stand, are taken out in successive to order and then set aside or stacked on a separate pipe rack.

During drilling procedures problems sometimes arise because the drilling mud, owing to inadequate or no cleaning at all, remains on the inside of the wall of the pipe sections after pull-out of the drill string during the tripping operation. The mud may thus dry and form hard flakes or clumps on the pulled-out pipe sections. When these pipe sections are to be redeployed, hard clumps or flake particles may be pumped down to the drill bit, and thus block one or more of its nozzles. In the worst case, the result of this is extensive damage to the drill bit, or also that problems arise in connection with, for example, downhole tools and motors.

Another drawback of inadequate removal of drilling mud during the tripping operation is undesired spillage of drilling mud on the deck of the drilling rig or in storage areas in the vicinity of the pipe rack. This causes unnecessary work cleaning the deck and disposing of the mud spillage, and, in the worst case, it could result in injuries due to a slippery and muddied deck.

To remedy the problems mentioned above, many alternative solutions are found in the patent literature, where, for instance, WO-A1 2006/006872 provides an example of wipers for internal removal of drilling mud from the drill string. In this case, the wiper is made having a mass and a volume that allow it to float on top of the drilling mud during the tripping operation. The wiper is bellows-shaped and comprises a weight that is connected to its upper part. Furthermore, the wiper is equipped with one or more channels past or through it so as to allow through-flow of the drilling mud. Reference is also made to this document as such for a closer understanding of the mode of operation of this type of wiper, without this thereby being regarded as limiting in respect of the use of other wiper types in the present invention.

Fishing tools that are used to retrieve equipment from a borehole are based on the equipment being secured in an appropriate manner downhole. The triggering mechanism in such fishing tools is therefore made to be screwed, forced over or to have gripping claws which require a hard blow for actuation. In this connection, there exist s breakable shear pins. Should the equipment in the borehole on the other hand be constituted of another type that is movable and thus not secured in a fixed position prior to retrieval, the traditional fishing tools are quite obviously unsuitable.

The wiper disclosed in WO-A1 2006/006872, which floats on the liquid column of io drilling mud inside the drill string, is a good example to illustrate equipment that is unsuitable for use with traditional fishing tools. In this case, it is most probable that the fishing tool will not manage to grip the fish neck on the wiper, but instead push it down into the drilling mud.

To solve this problem, there is proposed, according to the present invention, a fishing tool for cable-based retrieval of equipment from a borehole, characterised in that the tool comprises a seat cone, an inner spring that tensions the seat cone, a locking cone which is arranged externally to the locking cone and which is tensioned by an outer spring, and at least one latch that is pivotal into a position for gripping the equipment by movement of the seat cone and locking cone with the aid of the respective springs.

It is thus achieved that it is not only equipment which is fixed in the borehole that can be gripped in a reliable manner for retrieval to the surface, but also any other equipment that is movably mounted and therefore earlier could not be fished up without causing substantial problems during the fishing operation.

To facilitate the pivoting into the gripping position, the at least one latch can be mounted pivotally on a pivot, whilst the locking cone is arranged slidably on a sleeve, which at the lower end surrounds the seat cone.

Furthermore, to effect the gripping, the sleeve can be equipped with balls that are adapted to move from a recess in the lower end of the locking cone to a recess in the upper end of the seat cone. During this movement, the upper edge of each latch is pressed out when the locking cone is released and pressed downwards by the outer spring. Furthermore, the lower end of the seat cone is configured having a seat that is intended to rest against an upper end of the equipment for displacing the seat cone along the guide with simultaneous displacement of the locking cone in the opposite direction during actuation of the fishing tool for gripping the equipment.

Other advantageous features of the present invention are set forth in the dependent claims and in the description below.

A more detailed explanation of the present invention will be given below with reference to the appended drawings, wherein:

FIG. 1 is a schematic illustration of a set-up involving use of the fishing tool, for example, in connection with a drilling procedure;

FIG. 2 shows a schematic vertical section of the fishing tool in a neutral or loaded position before equipment is retrieved;

FIG. 3 shows the same as FIG. 1, but now in a position immediately prior to gripping the equipment;

FIG. 4 shows the same as FIG. 1, but now in a position for gripping the equipment; and

FIG. 5 is a schematic exploded perspective view of the fishing tool.

With reference to FIG. 1, the fishing tool, in a typical arrangement, is suspended from a cable 3 or the like inside, for example, a drill string 4 which has been passed through a turret 5. The cable 3 is let out or drawn in with the aid of a cable drum 6 with release brake and runs over a rack 7. The drum is shown here operated manually, but can of course instead be equipped with motor operation of a suitable type. Furthermore, the length of the cable determines how far down in the borehole, not illustrated, the fishing tool can be lowered for retrieval of the equipment 1. The cable is connected to the tool via, for example, an attachment means 25 in a top connector on the tool. See FIG. 3.

Details in connection with the fishing tool as such can be seen from FIGS. 2 to 5. As shown in FIG. 1, the tool comprises a seat cone 10 which is slidably mounted on a guide 20 which at an upper end is fastened in a suitable manner to the top connector 24. In the position that can be seen from FIG. 2, i.e., prior to catching the equipment 1 down in the borehole, the seat cone is pushed down by an inner spring 11 against a contact face that projects at the lower end of its guide. The seat cone is further configured at its lower end with a seat face 20 which is intended to trigger actuation of the tool when the seat face meets the upper end of the equipment. See FIG. 3.

Furthermore, the tool has a locking cone 12 which is arranged external to the locking cone, and which is tensioned by an outer spring 13, as shown in FIG. 2. The locking cone is arranged slidably on a sleeve 16 which at its lower end surrounds the seat cone. The downward movement of the locking cone for actuation of the fishing tool and subsequent gripping of the equipment 1 is effected by the outer spring. The sleeve is fastened at an upper end to the top connector 24 in any suitable way.

To be able to grip the equipment 1, the fishing tool is equipped with at least one latch 14 that is pivotally mounted to a pivot 15, in such a way that the latch pivots to the position that is shown in FIG. 4 by reciprocal displacement of the seat cone 10 and the locking cone 12 with the aid of the respective springs 11, 13. The lower end of the latch is configured with a profile that is adapted to be connected to a correspondingly shaped portion 2 at an upper end of the equipment 1 when it is gripped. The configuration of inclined faces in the profile facilitates, inter alia, the movement of the seat cone towards a bottom face of the sleeve 16 along which the locking cone 12 is simultaneously displaced. As shown in the drawings, the locking cone is equipped with a lower taper that is terminated in a substantially vertical portion. This thus causes a pivoting of the latch about the pivot prior to the resultant gripping of the equipment when the seat cone has been moved to the end position with the aid of the outer spring 13. See FIG. 4.

For maintaining the seat cone and locking cone 10, 12 in their respective end positions before and after actuation of the fishing tool, the sleeve 16 is equipped with balls 17. As shown in FIG. 2, the balls are located partly in a recess 18 at the lower end of the locking cone, and are then transferred in order partly to move to a recess 19 in an upper end of the seat cone (see FIG. 4) in the course of the reciprocal movement of the seat cone and the locking cone for the resultant gripping of the equipment by means of the at least one latch.

From the explanation above, it will be understood that the present invention provides a fishing tool that can easily be actuated simply by contact between the seat face and the upper end of the equipment that is to be fished for retrieval to the surface above the borehole. This contact causes the seat cone and locking cone to enter reciprocal displacement along the guide and the sleeve respectively by means of elastic force in the inner and outer spring. See FIG. 3. The result of this initial contact is thus that the at least one latch pivots from the original position in FIG. 3 to the gripping position in FIG. 4 for gripping the upper portion of the equipment that is to be recovered.

Although in the above reference was made to the wiper disclosed in WO-A1 2006/006872 as an example of relevant equipment for fishing, it will be understood that all other types of downhole tools, instruments and the like can be fished with the present tool. Furthermore, there is nothing to suggest that the tool according to the invention is necessarily only useful for use in connection with the retrieval of equipment which is freely movable in the borehole, as it is also conceivable that it can be used for equipment that is fixed in, for example, a drill string.

In addition, the fishing tool may in a non-illustrated way be equipped with:

-   -   a mechanism for releasing the fishing tool from the equipment if         a predetermined load/tension in the cable is exceeded, i.e., in         the event of an overload, or a time-determined release         mechanism.     -   a safety mechanism to prevent movement of the seat cone before         contact with the equipment is secured.     -   an adaptation to an internal or external profile on the         equipment. 

1. A fishing tool for cable-based retrieval of equipment from a borehole, wherein the tool comprises a seat cone, an inner spring that tensions the seat cone, a locking cone that is arranged external to the locking cone and which is tensioned by an outer spring, and at least one latch that is pivotal to a position for gripping the equipment by movement of the seat cone and locking cone with the aid of the respective springs.
 2. A fishing tool according to claim 1, wherein the at least one latch is pivotally mounted on a pivot.
 3. A fishing tool according to claim 1, wherein the locking cone is arranged slidably on a sleeve which at a lower end surrounds the seat cone.
 4. A fishing tool according to claim 1, wherein the seat cone is slidably mounted on a guide.
 5. A fishing tool according to claim 4, wherein a lower end of the seat cone is configured with a seat that is intended to rest against an upper end of the equipment for displacement of the seat cone along the guide with simultaneous displacement of the locking cone in the opposite direction during actuation of the fishing tool for gripping the equipment.
 6. A fishing tool according to claim 1, wherein the sleeve is equipped with balls that are adapted for moving from a recess in a lower end of the locking cone to a recess in an upper end of the seat cone.
 7. A fishing tool according to claim 1, wherein the at least one latch is provided with profiling that is adapted to be connected to a correspondingly shaped portion on an upper end of the equipment when gripping the equipment.
 8. A fishing tool according to claim 1, wherein the tool comprises an outer housing consisting of an upper tubular piece and a lower tubular tip.
 9. A fishing tool according to claim 8, wherein an upper end of the tubular piece of the housing is fastened to a top connector equipped with an attachment means for a fishing cable. 